Smoking in movies rated PG-13 seems to have the biggest impact on teen and tween experimentation with tobacco, researchers found.

Kids 10 to 14 years old were 49% more likely to have tried a cigarette for every 500 they saw smoked on the screen in PG-13 movies, James D. Sargent, MD, of Dartmouth-Hitchcock Medical Center in Lebanon, N.H., and colleagues found.

The risk was 33% elevated with the same amount of exposure to smoking in R-rated movies, the group reported in the August issue of Pediatrics.

Fully overlapping confidence intervals for the two motion picture ratings (both supporting a hazard ratio of 1.23 to 1.81) suggested “it is the movie smoking that prompts adolescents to smoke, not other characteristics of R-rated movies or adolescents drawn to them,” they wrote.

But smoking in movies rated and oriented toward kids didn’t appear to have the same negative impact in that survey, or in a separate study appearing alongside it in Pediatrics.

However, the authors pointed out that the studies could not prove a causal link between smoking in movies and smoking experimentation by adolescents.

The Motion Picture Association of America defines a PG-13 movie as one where parents are “strongly cautioned. Some material may be inappropriate for children under 13.” An R-rated movie is restricted and children under age 17 must be accompanied by a parent or adult guardian.

Because the majority of exposure came from smoking in PG-13-rated films, giving movies an R rating for showing smoking could substantially cut down on underage smoking, Sargent’s group recommended.

Based on the effect size and attributable risk determined in their survey, stubbing out smoking in PG-13 movies to what the least exposed 5% of kids see would be expected to reduce adolescent smoking by 18%, the authors suggested.

They believe the effect would be similar to what would happen if all parents became maximally authoritative in their parenting, projected as a 16% reduction with overlapping confidence intervals.

The survey included 6,522 adolescents in a longitudinal study with rounds of follow-up every 8 months over a 2-year period in which they reported which movies they’d seen and whether they’d tried a cigarette.

Based on total tabulated smoking events, the median exposure of the survey group was 275 occurrences of smoking in PG-13 movies and 93 in R-rated movies.

The “high-dose” group, at the 95th percentile for exposure to smoking in movies, had watched a median of 894 occurrences of smoking in PG-13 movies and 1,002 in R-rated movies.

Smoking instances seen in G- and PG-rated movies were lower, at a median of 61, and had no correlation with likelihood of having tried a cigarette (adjusted hazard odds ratio 0.49, 95% CI 0.22 to 1.09), though underpowered to detect a small difference.

In a second paper, Sargent, along with a group of Dutch researchers led by Kirsten Lochbuehler, MSc, of Radboud University Nijmegen, the Netherlands, conducted experiments to test whether smoking in kid-rated movies impacted attitudes.

They randomized one group of 101 children (ages 8 to 10) and another of 105 kids (ages 8 to 11) to watch a cartoon or family-oriented film for 20 minutes that contained no smoking or one in which characters smoked.

Most kids in both groups reported negative views on smoking, and which movie they watched had no impact on general attitude toward smoking, whether they expected to be a smoker, or other measures.

The only statistically significant effect was on perceived social norms, with a shift away from anti-smoking (P=0.04).

While reassuring for parents that a little exposure had only a small impact on smoking beliefs, “a significant cumulative impact on norms cannot be ruled out,” the researchers wrote.

“A single movie may not affect beliefs about smoking, but this study begs the question of just how many depictions of smoking in movies constitute the turning point,” they added.

Neither study should be used as a justification to add more scenes with smoking into G- and PG-rated movies, the investigators cautioned.

Primary source: Pediatrics
Source reference: Sargent JD, et al “Influence of motion picture rating on adolescent response to movie smoking” Pediatr. 2012; DOI: 10.1542/peds.2011-1787.

Additional source: Pediatrics
Source reference: Lochbuehler K, et al “Influence of smoking cues in movies on children’s beliefs about smoking” Pediatrics 2012; DOI: 10.1542/peds.2011-1792.